The technology of producing sustained-release microcapsules from a W/O emulsion utilizing a biodegradable polymer is described in, inter alia, JP-A57-118512 and JP-A57-150609.
However, a method of producing sustained-release microcapsules containing a biologically active substance which comprises heating microcapsules at a temperature not lower than the glass transition temperature of the biodegradable polymer but not so high as to cause aggregation of the microcapsules has not been described in the references noted above.
Any sustained-release microcapsule having a biodegradable polymer shell preferably minimizes the initial burst release of the active ingredient to particularly protect against overdosing within one day following administration, and yet adapted to release the active ingredient at a calculated rate over a protracted time period. However, the sustained release-microcapsules heretofore available have the drawback of an initial burst within the day of administration and are, therefore, not fully satisfactory.